This invention relates to antiparasitic agents and in particular to compounds related to the avermectins but having a novel substituent group at the 25-position and to processes for their preparation and compositions thereof.
The avermectins are a group of broad spectrum antiparasitic agents referred to previously as the C-076 compounds. They are produced by fermenting a strain of the microorganism Streptomyces avermitilis under aerobic conditions in an aqueous nutrient medium containing inorganic salts and assimilable sources of carbon and nitrogen. The isolation and the chemical structure of the eight individual components which make up the C-076 complex is described in detail in British Patent Specification No. 1573955.
European Patent Applications Nos. 0214731, published Mar. 18, 1987, and 0284176, published Sept. 28, 1988, and U.S. application Ser. No. 249,749, filed Sept. 27, 1988, describe preparation of compounds related to the avermectins but having an unnatural substituent group at the 25-position in place of the isopropyl or sec-butyl group which is present in the naturally occuring avermectins.